1. Related Field
This invention relates to the operation of vehicle controls.
2. Related Art
In a vehicle such as an automobile, the driver can typically operate a control device to influence the power output of the vehicle. Conventionally this device takes the form of a pedal which is sprung upwards to a default position and can be depressed from that position by the driver's foot, but other devices such as hand-operated levers can be used for the same purpose. In older vehicles the control device was mechanically linked to a throttle valve that regulated the power output of the vehicle's engine, and for that reason the device is conventionally known as a throttle. However, in modern vehicles the throttle control normally controls the behaviour of the car as one of a number of electrical inputs to an engine control unit (ECU). The throttle control may also be known as an accelerator.
In a vehicle that is operated via an ECU, the ECU receives a number of inputs and processes those inputs in accordance with a pre-stored control strategy in order to form a series of outputs which regulate the operation of the vehicle. For illustration, in the case of a vehicle powered by an internal combustion engine the inputs could include throttle position, engine RPM (revolutions per minute), inlet air temperature and selected drive gear; and the outputs could include the amount of fuel to be dispensed into the engine's cylinders, the level of turbo boost to be applied and the engine's ignition timing. The pre-stored control strategy allows the ECU to determine, for a particular set of inputs, the output values that will be used to regulate the vehicle.
A commonly used control strategy is to establish a fixed relationship between throttle position and torque demand. With such a strategy, the torque demand can be determined in dependence on throttle position, so in response to the throttle position the engine can be regulated in such a way as to generate the appropriate level of torque. The outputs required to generate a given level of torque can be established when the vehicle is being designed.
One example of such a strategy is illustrated in FIG. 1. FIG. 1 shows a plot of throttle position on the X axis against torque demand on the Y axis. In FIG. 1 torque demand is expressed as a percentage of the maximum output torque of the engine. In this example there is a linear relationship between throttle position and torque demand. This relationship gives a smooth driving feel. To give a sportier driving feel a strategy such as that in FIG. 2 can be used. In this strategy the relationship between throttle position and torque demand is non-linear. A given change in throttle position causes a greater change in torque demand at lower throttle positions (region 1) (i.e. when the throttle is closer to its resting or low demand position) than at greater throttle positions (region 2) (i.e. when the throttle is further from its resting or low demand position).
During an acceleration event where the throttle starts from a low or default (e.g. 0% travel) position, the strategy of FIG. 2 can makes a vehicle feel more responsive because a relatively large change in torque will be produced for small movements of the throttle from its starting position. However, during a deceleration event where the throttle starts from a high position it has the disadvantage that it can make the vehicle feel less responsive because a relatively small change in torque will be produced for small movements of the throttle from its starting position. If the driver has accelerated hard and has advanced the throttle to the 90% position, when he then releases the throttle to, say, the 60% position he will feel relatively little retardation of the vehicle.
There is a need for a way of controlling a vehicle that can provide a sporty feel for increasing throttle positions with a reduced associated loss of responsiveness for decreasing throttle positions.